The 802.3 Ethernet protocol has experienced a rapid advancement since born, and currently has become an undisputable actual standard within the LAN (Local Area Network) domain. Transport means for this protocol developed from the initial 10M (Megabit) with thick-cable bus to the 10Base2 with thin-cable, further to the 1Base5 and the 10Base-T with twisted-pair, still further to the 100Base-TX transported with Ethernet Category-5 line, the 100BaseT4 transported with Ethernet Category-3 line and the 100BaseFX transported with optical fiber, and subsequently to the Gigabit Ethernet including the 1000Base-SX transported with short-wavelength light, the 1000Base-LX transported with long-wavelength light and the 1000Base-T transported with Category-5 line. The IEEE (Institute of Electrical and Electronics Engineers) approved a standard for 802.3ae 10 Gbps Ethernet (10 GE) in 2002.
The 10 GE technology is a “high-speed” Ethernet technology, which is compatible with conventional Ethernet modes and takes advantage of the same MAC (Media Access Control) protocol, length-variable frame format and minimum and maximum frame lengths (a 64 to 1514-byte packet) as the conventional Ethernet modes. The operating rate defined by the 802.3ae for the MAC in the 10 GE is a standard one of 10 Gbps, and two forms of Physical Layer (PHY), LAN PHY and WAN (Wide Area Network) PHY can be used for transport. The LAN PHY provides a transport rate matching the 10 G MAC, and has a rated line rate for its operation of 10.3125 Gbps (i.e. a rate of 64B/66B-encoded 10 Gbps traffic data), and the WAN PHY provides a transport interface for seamless connection with the existing SDH (Synchronous Digital Hierarchy), and provides a traffic data transport rate of 9.58464 Gbps with the OC192C frame format.
With the continuous increase of demanded traffic transport bandwidths, applications of the OTN tend to be popular. It is an important issue how to transport the 10 GE traffic directly through the OTN with high quality and efficiency. There exists an inherent difference between line rates of the 10 GE and the OTN. As mentioned previously, the operating rate of the 10 G MAC is a standard one of 10 Gbps, and 10.3125 Gbps after being encoded through physical layer, and in the OTN, a payload of an OPU2 (Optical channel Payload Unit) is provided with a rated data rate of 9,995,276,963 bps (approximately referred to as 9.9953 Gb/s hereinafter for brevity), which consequently makes it difficult to enable the seamless transport of data between the networks.
At present, there are several solutions for mapping the 10 GE traffic to OTU2s (Optical channel Transport Units, generated from standard encapsulation of OPU2s in compliance with the ITU-T G.709 standard) in the OTN:
1. With the use of a 10 GE WAN interface, the 10 GE traffic is first processed into the OC192C frame format through the existing WIS (WAN Interface Sub-layer) in the WAN PHY, which is then mapped to OTU2s.
2. With the use of a 10 GE LAN interface, Ethernet packets are first converted into GFP packets with a flow control through the GFP (Generic Framing Procedure) with a flow control, which are then mapped to OTU2s.
3. An interface between the 10 GE-LAN and the SDH network, which is implemented through the GFP with a flow control, is further mapped to OTU2s.
4. With the use of a 10 GE LAN interface, Ethernet packets are first converted into GFP packets, through the GFP without a flow control, which are then mapped to OTU2s, where seven OPU2 OH (OverHead) bytes are needed.
5. With the use of a 10 GE LAN interface, the 10 GE traffic is directly mapped to OTU2s. Since the data rate of the 10 GE traffic is slightly higher, this solution needs to occupy partial FEC (Forward Error Correction) bytes of an OTU2, thus degrading the gain of the FEC.
6. With the use of a 10 GE LAN interface, the 10 GE traffic is directly mapped to extended OTU2s. This solution uses OTU2s with more than 4080 columns instead of standard OTU2 frames, and resulting in an outputting rate of 11.1 GHz for OTU signals, instead of a standard 10.7 GHz in the industry.
The solutions 1 through 4 described above each implement the mapping of the 10 G MAC packets to the OTU2 frames through two or more mapping procedures, which increases the complexity of devices in terms of their physical designs and relies upon a complex encapsulation technology for encapsulation of the 10 G MAC packets into intermediate data packets in compliance with a certain standard. The solutions 5 and 6 can directly enable through a PHY the transparent transport of the 10 GE traffic to the OTN, but have to either occupy a certain part of the FEC for transport of the 10 GE traffic or extend the OTU2 frames, thus resulting in a breach of the standard form of the OTU2 frames and in a significant obstacle to interfacing different chips. Moreover, the solution 5 has to employ a more complex enhanced FEC to ensure the coding gain of the FEC, and thus fails to simultaneously obtain both efficiency and transport quality, and the solution 6 is non-standardized, and thus can not be adapted smoothly to a future 40 Gbps transport circumstance, because some OTUs are in 10.7 GHz and others are in 11.1 GHz, so that numerous OTUs from different users can not be combined together through multiplexing them. Obviously from the above, the existing various processing methods have their respective disadvantages, and are prone to giving rise to an isolated network “island”, which makes it difficult to interface networks and share information.